Various methods have been used to cast aluminum products. Examples of the methods include: gravity die casting; and low-pressure casting in which molten metal is poured into a casting cavity by being lifted against gravity. In addition, die casting in which molten metal is poured (injected and filled) into a casting cavity at high speed with high pressure has been known as a technique for making accuracy of dimensions and productivity better than the above-mentioned casting methods. Die casting has been used as an aluminum product manufacturing method as well. A familiar variant of die casting is pore-free die casting, which has been used to prevent gas porosity defects from occurring due to trapping air in the cavity.
In general, aluminum disc brake calipers (hereinafter referred to as brake calipers) have been manufactured by use of the gravity casting method as shown in Patent Literature 1, for example. There is also a document such as Patent Literature 2 which suggests manufacture of brake calipers using die casting, but this document does not state a specific manufacturing method thereof.
The brake caliper has a complicated shape in which: the brake caliper includes opposing portions opposed to each other with a housing space (a hollow portion) for housing a disc being interposed in between, and connecting portions connecting the opposing portions at two sides thereof, respectively; and a cylinder portion into which a piston can be fitted is formed in each of the opposing portions.
In addition, higher final dimensional accuracy is required for the brake caliper, because the brake caliper is configured to stop the disc in high-speed rotation by sandwiching the disc by brake pads attached to the pistons. For this reason, if the brake caliper is manufactured using die casting which enables casting with higher dimensional accuracy, the number of final finishing processes can be reduced. In this context, the realization of the manufacture of the brake caliper using die casting has been awaited.